The present invention relates to a photo-crosslinkable light-sensitive composition capable of being crosslinked through a cyclization-addition reaction and more specifically to a light-sensitive composition which comprises a photo-crosslinkable polymer having a maleimido group at a side chain and a novel sensitizer, in particular to a light-sensitive composition useful for preparing a light-sensitive layer of light-sensitive lithographic printing plates, photoresist layers, or the like.
Photo-crosslinkable materials which are cross-linked through a cyclization-addition reaction have been well known and been used as a main component of light-sensitive compositions for making light-sensitive lithographic printing plates (hereunder referred to as "PS plates"), photoresists and the like. Among these crosslinkable materials, photo-crosslinkable polymers having a maleimido group at a side chain do not exhibit sufficient light-sensitivity and, therefore, a sensitizer such as thioxanthones, benzophenones, Michler's ketones, anthraquinones, anthracenes, chrysenes, p-dinitrobenzenes or 2-nitrofluorenones has been used as a sensitizer to enhance the light-sensitivity of such polymers. The light-sensitivity of the polymers is enhanced by the addition of such a sensitizer, but is still insufficient. Moreover, since it takes a long period of time to conduct imagewise exposure for forming images, the workability thereof is insufficient and images of good quality cannot be reproduced if there is slight vibration in the operations for obtaining fine images.
In addition, these sensitizers only absorb light having short wave length and its .lambda..sub.max is at most about 400 nm. Therefore, light sources are much limited for exposing the composition containing such sensitizers.
To eliminate the foregoing disadvantages, it has been proposed to use, as a sensitizer, a compound represented by the following general formula: ##STR2## (in the formula, Z represents a group of nonmetallic atoms required for forming a heterocyclic nucleus including a nitrogen atom and R represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic ring) in Japanese Patent Unexamined Publication (hereunder referred to as "J.P. KOKAI") No. Sho 62-294238.
However, these sensitizers also absorb only light having a short wave length and the .lambda..sub.max thereof is at most about 400 nm. Moreover, the sensitivity thereof is still insufficient.